The protection of crops from weeds and other vegetation which inhibit crop growth is a constantly recurring problem in agriculture. To help combat this problem, researchers in the field of synthetic chemistry have produced an extensive variety of chemicals and chemical formulations effective in the control of such unwanted growth. Chemical herbicides of many types have been disclosed in the literature and a large number are in commercial use.
In some cases, herbicidal active ingredients have been shown to be more effective in combination than when applied individually and this is referred to as “synergism.” As described in the Herbicide Handbook of the Weed Science Society of America, Seventh Edition, 1994, p. 318, “‘synergism’ [is] an interaction of two or more factors such that the effect when combined is greater than the predicted effect based on the response of each factor applied separately.” The present invention is based on the discovery that certain cereal or rice herbicides and certain pyridine or pyrimidine carboxylic acids, already known individually for their herbicidal efficacy, display a synergistic effect when applied in combination.
The herbicidal compounds forming the synergistic composition of this invention are independently known in the art for their effects on plant growth.